Conventional vehicles, in particular hybrid, electric, or hydraulic vehicles, may have at least two drive units, at least a first of the two drive units being able to be coupled to the power train via various mechanical couplings. Upon the change of this mechanical coupling, e.g., upon coupling or decoupling of a drive unit or to shift a transmission, i.e., to change the transmission ratio of a transmission, a power or torque influence of the first drive unit and the further drive units takes place.
A change of the mechanical coupling of a drive unit typically takes place with the aid of friction-locked or form-locked clutches. Form-locked clutches typically may not be operated under load. They require completely load-free shifting, i.e., a torque influence up to the torque freedom of the drive unit and speed synchronization between the primary side and the secondary side of the clutch.
German Patent Application No. DE 101 26 348 A1 describes performing a torque influence of a further drive unit upon a change of the mechanical transmission ratio of a transmission of a first drive unit. During the shifting of the automated manual shift transmission on the main power train, the torque is equalized using a secondary system, so that no change of the acceleration is perceived by the driver. The difference between the torque requested by the driver and the torque achieved by the transmission is compensated for by the secondary system during shifting.
To change the coupling of a drive unit, which is designed as an electric machine, from an engaged first clutch to an engaged second clutch, the following steps are performed. A torque influence of the electric machine initially takes place, i.e., a torque reduction or a buildup is carried out in order to achieve the load-free condition. In a further step, the torque influence of the further drive unit is carried out simultaneously. This is carried out by the second drive unit by assuming the torque fraction reduced or built up at the electric machine, in order to continue to generate a predefined total setpoint torque. The first clutch is then disengaged. Subsequently, a speed synchronicity is produced on the primary side and the secondary side of the second clutch by torque influence or speed regulation of the electric machine, which corresponds to an active speed synchronization. If this speed synchronicity is achieved, the second clutch is engaged. The torque of the second drive unit is subsequently influenced in such a way that the reduction of the torque fraction built up by the electric machine takes place at the second drive unit (or vice versa), in order to continue to generate a predefined total setpoint torque. This corresponds to a redistribution of the torque from the second drive unit to the electric machine.